Picky songbirds demand native oaks

Dan Airola pays attention to birds. That led him to pay more attention to trees.

In particular, Airola has been scouting native oaks – especially Sacramento’s iconic valley oaks – to see who eats what and where. His results show a resourcefulness among the area’s bird population as well as the importance of native species.

And he hopes his research may prompt Sacramento area homeowners to plant more native oaks – or at least value the ones they still have.

Birds are the wildlife that urban residents see most, especially along the Pacific Flyway. Millions of birds pass through the Sacramento Valley each winter. That’s made bird watching a popular local pastime, as well as inspired the 11th annual Galt Winter Bird Festival, set for Saturday, Jan. 20.

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In addition to the winter flocks of water fowl, songbirds visit Sacramento during their seasonal migrations while other birds stay here year-round.

A wildlife biologist and trained ornithologist, Airola has been an observant bird watcher for decades. His past study of turkey vultures in Land Park helped explain why hundreds of these huge birds tended to congregate in one location (much to some residents’ chagrin).

Watching wildlife near his Sacramento home, Airola noticed migratory songbirds tended to prefer valley oaks to other trees. He teamed with UC Davis professor Steve Greco, an urban ecology expert, to do a formal study, centered in Airola’s Curtis Park neighborhood – home to valley oaks that are centuries old.

“Our study has shown that a surprisingly large number of migratory songbirds use valley oaks as foraging stopover sites during the fall and spring migrations,” Airola said. “The group of affected species includes a wide range of colorful warblers, vireos, tanagers, flycatchers and grosbeaks.”

These “feathered jewels” – the kind of visitors that get birdwatchers excited – have an appetite for certain kinds of insects. They find those on native oaks. On non-native ornamental trees? Not so much.

“Presumably, this high use is a result of a more abundant and diverse insect fauna on the native oaks,” Airola explained. “In contrast, non-native trees were brought here without the insect species that adapted to them in their native lands.”

Populations of migratory songbirds have been on a steady decline, Airola noted. A result of urban development, fewer trees with the right insects may be part of that impact. Replacing natives oaks with the same species while also preserving remaining oaks could buoy bird counts.

“We think these results have important applications for urban forestry and homeowner landscaping,” he said.

The relationship of native oaks and birds predates the valley’s people, who cut down countless oaks.

“Much of the native valley oak woodlands in the (Sacramento) Valley are gone, leaving only their namesake towns such as Woodland and Elk Grove,” Airola said. “The seasonal use of oaks by these (migrant songbirds) likely dates back for eons, and loss of oaks may have contributed to well-documented declines in many species populations. Valley oaks represent only a very small proportion of the trees being planted in the urban forest today.”

Native oaks also play a vital role for year-round resident birds, such as the California Scrub Jay. Airola is in the midst of a separate study on jays and their adaptation to an urban environment.

“It started by watching the jays near my home, seeing their behavior,” Airola said. “Something was going on here – but what? That’s what got me started.”

Bird watchers tend to overlook bird behavior close to home, he added.

“Even to bird watchers, they don’t know about these things,” he said. “Most bird watchers don’t spend much time birding in urban areas; they go out to the wetlands or other areas with lots of birds.”

Airola found that scrub jays adapt to urban areas with fewer oaks by flying – and hiding – acorns hundreds of yards from the source. In wild settings, scrub jays stay close to their home groves of closely packed oaks.

“The California Scrub Jay is a real oak user,” he said. “Acorns are so important to them. Each individual bird will transport up to 7,000 acorns a year and cache them. By trying to follow them, I found they could go 1,600 feet to hide an acorn.”

Substitute non-native oak species (such as cork oak) don’t provide the same diet to birds and attract a lot fewer feathered friends, he added.

Native oaks make sense for people as well as birds, notes the Sacramento Tree Foundation, a longtime advocate.

“Native oaks are a great choice for Sacramento, given adequate space and appropriate care,” said Zarah Wyly, restoration ecologist for the Sacramento Tree Foundation.

Since its inception in 1982, the foundation has planted at least 50,000 native oaks, she said. It has several partners in this effort. Sacramento County plants oaks in larger parks and open spaces to replace trees lost to development. SMUD offers deciduous native oaks as shade trees to customers.

Hundreds of Sacramento area third-graders take part in the foundation’s Seed to Seedling program to gather, sprout and grow acorns into seedling trees to plant at local residents’ homes or at parks and schools.

Besides their benefits to birds, native oaks have a lot to offer people and other animals, Wyly said.

“We plant native oaks for a variety of reasons,” Wyly said. “They are adapted to our climate and are very drought tolerant. They are beautiful and connect us to our historical landscapes. They are very important to support our native wildlife and fill an important role in the life histories of at least 310 vertebrate species and 5,000 insects.”

Planted in the right place, valley oaks can help save money and help the environment, too.

“They are large and long-lived trees,” Wyly added, “which make them well-suited to provide us maximum benefits in regards to shade, urban heat island effect mitigation, air quality improvement, stormwater retention and erosion mitigation, as well as a variety of public health associated benefits.”

Assumptions about native oaks keep people from planting more, said Airola, while examining a 200-year-old giant along Markham Way. “There are so many myths about oaks: They’re slow-growing, they’re messy, they tend to fall over. It takes an oak a long time to get to the size of this one. During our lifetimes, a newly planted oak will be a much smaller tree, but still benefit birds.”

Airola hopes that his observations prompt more people to take a second look at oaks.

“My work is as much about urban forestry as birds,” Airola said. “Providing food sources for wildlife is vital. We now have a bare remnant of our old forest. We may plant new trees, but we haven’t replaced our oaks. That could determine the ultimate populations of the birds.”